JPS61280163A - Method for determining condition of reading radiation picture information - Google Patents

Abstract

PURPOSE:To determine condition of reading most suitable especially for diagnosing osseous parts and improve capacity of diagnosing by determining the condition of reading basing on the part of histogram ranging from minimum value of the quantity of light of accelerated phosphorescence to a specified value determined according to the condition of photographing out of advance reading histogram. CONSTITUTION:An advance reading histogram is obtained by advance reading, and condition of reading is determined basing on the part L of the histogram ranging from the minimum quantity of light emission of accelerated phosphores cence S1 to a specified quantity of light emission of accelerated phosphorescence determined according to the condition of photographing. Maximum and minimum quantity of light emission of accelerated phosphorescence Smax and Smin (Smin =S1) of the part of histogram L are determined. The range of input signal level (Qmax-Qmin) to a picture processing device corresponding to proper range of density (Dmax-Dmin) is determined univocally according to this condi tion of gradation processing. Accordingly, the condition of reading is determined to make Smax and Smin correspond to Qmax and Qmin.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a radiation image information reading condition determination method used in a radiation image information recording and reproducing system used for medical diagnosis and the like.

When certain types of phosphors are irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a portion of this radiation energy is accumulated in the phosphor, causing the phosphor to emit visible light. It is known that when irradiated with excitation light such as, phosphors exhibit stimulated luminescence depending on the accumulated energy, and phosphors exhibiting such properties are called stimulable phosphors.

Using this stimulable phosphor, radiation image information of a subject such as a human body is partially recorded on a sheet of stimulable phosphor, and this phosphor sheet is scanned with excitation light such as a laser beam to emit stimulated light. A radiation image information recording and reproducing method that generates light, reads the obtained stimulated luminescence light in a charging manner to obtain an image signal, and outputs it as a visible image to a recording material such as a photographic light-sensitive material, CRT, etc. based on this image signal. A system has already been proposed by the applicant. (Unexamined Japanese Patent Publication No. 55-12429, No. 56-
No. 11395 etc. ) As one aspect of the above-mentioned number l>1-line image information recording and reproducing system, a stimulable phosphor sheet on which radiation image information of a subject is stored and recorded using radiation energy level as a medium is scanned with excitation light, and this scanning causes the above-mentioned Is the stimulable luminescent light emitted from the sheet light? Prior to reading by the I-reading means to obtain an electrical image signal for visible image reproduction, the sheet is scanned in advance with excitation light of a lower level than the excitation light used for this reading to accumulate and record on this sheet. Perform pre-reading to read the outline of the image information obtained by this pre-reading, determine reading conditions for performing the main reading based on the image information obtained by this pre-reading, perform the main reading according to the reading conditions, and read the main reading obtained by this main reading. The image signal is input to an image processing means, and the image processing means processes the image signal so as to obtain an output image suitable for the purpose of diagnosis according to the region to be photographed, the method of photographing, etc. A system for reproducing a visible output image is known, for example, as disclosed in Japanese Patent Application Laid-Open No. 58-67240, which was previously filed by the present applicant and has already been published.

The present invention relates to a method used in a radiation image information recording and reproducing system that performs the above-mentioned pre-reading and main reading, and relates to a method of determining reading conditions for main reading based on image information obtained by pre-reading.

Here, reading conditions are a general term for various conditions that affect the relationship between the amount of stimulated luminescence light and the output of the reading device during reading, such as reading gain, scale factor, or , the power of excitation light during reading, etc.

(Technical Background of the Invention) As mentioned above, in a radiation image information recording and reproducing system using a stimulable phosphor sheet, prior to reading to obtain an electrical image signal for reproducing a visible output image from the stimulable phosphor sheet. Understand the outline of the image information accumulated and recorded on the sheet in advance, determine appropriate reading conditions based on this, perform the main reading according to these reading conditions, and grasp the outline of this image information in advance. As one method for this, the applicant has already proposed a pre-reading method in which the sheet is scanned with excitation light at a lower level than the excitation light used during main reading, and the stimulated luminescence light emitted from the sheet is read by this scanning. has been done.

Note that the excitation light used for pre-reading is at a lower level than the excitation light used for main reading because the effective energy of the excitation light that the stimulable phosphor sheet receives per unit area during pre-reading is lower than the excitation light used for main reading. means smaller than that of . As a method of making the excitation light of the pre-reading lower than the excitation light of the main reading, there is a method of reducing the output of the excitation light source such as a laser light source, a method of reducing the output of the excitation light source such as a laser light source, and a method of using an NO filter, AOM, etc. in the optical path of the excitation light emitted from the light source. A method of attenuation, a method of providing a light source for pre-reading and a light source for main reading separately and making the output of the former smaller than the output of the latter, and a method of increasing the beam diameter of the excitation light,
Examples include a method of increasing the scanning speed of excitation light and a method of increasing the transport speed of the stimulable phosphor sheet.

In this way, by grasping the outline of the image information stored on the sheet before the actual reading and performing the actual reading according to the reading conditions determined based on the outline of this image information, it is possible to This eliminates the inconvenience caused by fluctuations in the range of radiation energy levels accumulated and recorded on the sheet due to fluctuations in radiation exposure, etc., and provides the effect that main reading can always be performed under desirable reading conditions.

Various methods can be considered for determining the reading conditions by grasping the outline of the image information in advance through pre-reading as described above, but one method is to obtain a histogram of the amount of stimulated luminescence obtained by pre-reading, and One possible method is to determine the reading conditions based on the histogram.

As one aspect of the method of determining the reading conditions based on the above-mentioned histogram, for example, the maximum stimulated emission light amount Smax and the minimum stimulated emission light amount 3m1n of the desired image information range in the histogram are determined, and the 3maX and 3m1n are determined.
The reading conditions are set so as to correspond to the maximum signal level QmaX and the minimum signal level Qmin of the desired input signal range in the image processing means, which are respectively determined by the maximum density □max and minimum density pmin of the appropriate In range in the visible output image. There is a method for determining this, and this method has been patented by the present applicant (Japanese Patent Application No. 12658/1982) on January 26, 1982.

However, in the above method, the maximum stimulated luminescence light amount in the desired image information range in the above histogram is 3 wa
The reading conditions determined by how x and the minimum stimulated light emission amount 3 sin are determined, in other words, which range on the histogram is the desired image information range, change, and the output image also changes at 11 degrees. , contrast, etc. change.

Therefore, when using the method of determining reading conditions based on the desired image information range of the above-mentioned histogram, the reading conditions must be adjusted based on various circumstances, especially in order to obtain an output image with optimal density, contrast, etc. for diagnostic purposes. Determine.

In other words, it is necessary to determine the desired image information range on the histogram so that such reading conditions can be obtained.

(Purpose of J. Akira) In view of the above circumstances, an object of the present invention is to provide a method for determining reading conditions based on a desired image information range portion of a read-ahead histogram, which provides optimal reading conditions particularly for bone diagnosis. The purpose is to provide a method for determining the

(Structure of the Invention) Broadcast QiJ411ii according to the present invention! In order to achieve the above-mentioned purpose, the 1III information reading condition determination method determines the reading conditions from a part of the pre-read histogram, that is, from the minimum value of the stimulated luminescence light amount to a predetermined value determined by the photographing conditions (this range is (corresponds to the desired image information range above)
It is characterized in that the determination is made based on a histogram portion extending over the range, that is, a histogram portion existing within a range of a predetermined width determined by the photographing conditions from the minimum value to the maximum value side.

The above-mentioned imaging conditions refer to conditions that characterize a solid body, and representative examples include the region to be imaged and the imaging method. The part to be photographed is the part of the subject to be photographed, such as the head,
It refers to the chest, abdomen, etc., and the imaging methods include simple imaging, contrast imaging, tomography, and magnification imaging.

The minimum stimulated light amount in the above histogram refers to the true minimum stimulated light amount on the histogram, the minimum stimulated light amount determined by a predetermined threshold, and the remaining irradiation field histogram excluding the scattered radiation histogram portion. It also includes the minimum amount of stimulated light emission in that part.

Note that the determination of the reading conditions is not limited to the case where the reading conditions are determined based only on the above-mentioned histogram part, but also includes the case where the reading conditions are determined in rough consideration of the imaging site, the imaging method, and the like.

(Effects of the Invention) As described above, the method according to the present invention determines reading conditions based on the histogram portion of the pre-read histogram that ranges from the minimum value of the amount of stimulated luminescence to a predetermined value determined by the photographing conditions. Therefore, it is possible to easily determine the optimal reading conditions especially for bone diagnosis.
In the case of bone diagnosis, the effect is that the diagnostic ability can be improved.

That is, when attempting to diagnose a bone by photographing a limb, for example, it is assumed that the photographed stimulable phosphor sheet is read in advance and a histogram as shown in FIG. 1 is obtained. In this pistogram, part A, which has the largest amount of stimulated luminescence light, is the bare part, that is, the part where the radiation directly enters the stimulable phosphor sheet without passing through the subject, and the next part B is the skin and the part close to the skin. , the remaining part 0 is subcutaneous tissue parts such as bones and muscles. That is, in the histogram of the photostimulated luminescence amount, the above-mentioned plain number part A and the skin part B generally exist in the high photostimulated luminescence quantity region, and in the case of diagnosis of bone parts, these blank parts are part A and the skin part B. Part B information is not required. Therefore, when determining the reading conditions, it is necessary to read only the remaining 0 parts except for area A and skin area B. In other words, this 0 part should be set at an appropriate density interval suitable for observation and interpretation in the output image ( If it is read so that it is displayed over the entire area (Dwax - □atn), the contrast of the bone region will be improved, and the diagnostic ability can be further improved. On the other hand, in such a case, the histogram shows how much of the subcutaneous tissues such as bones and muscles are present from the minimum amount of stimulated luminescence, or how much of the stimulated luminescence is beyond the minimum amount of stimulated luminescence. It is possible to know in advance whether the light amount area is the skin or bare skin based on information on imaging conditions such as the area to be imaged and the imaging method. Therefore, according to the present invention, by determining the reading conditions based on the histogram portion of the pre-read histogram that ranges from the minimum value of the amount of stimulated luminescence to a predetermined value determined by the imaging conditions, bone It is possible to determine the reading conditions so that the information on the bones and skin parts that are unnecessary for diagnosis is cut out, and the information on the necessary bones and surrounding parts is mainly displayed in the output image. As a result, the bone parts are displayed with a higher density and greater contrast, making it easier to see, and the ability to diagnose the bone parts can be improved.

(Actual FM Mode) Hereinafter, with reference to the drawings, the actual FM mode of the method according to the present invention will be explained.
The aspect will be explained.

In this case, Mr. B uses pre-reading to obtain a pre-read histogram as shown in Fig. 1, and in this histogram, a histogram covering the range from the minimum stimulated luminescence light It S t to a predetermined stimulated luminescence light amount determined by the photographing conditions is calculated. Determine reading conditions based on the partial size.

The minimum stimulated luminescence light amount S1 may be the true minimum stimulated luminescence light quantity as shown in FIG. 1, or may be a value determined by a predetermined threshold value Tl as shown in FIG. As shown in FIG. 3, if there is a noise component due to scattered rays in the region of low stimulated luminescence light quantity, the noise component may be removed and the minimum stimulated luminescence light quantity of the histogram portion may be used. When the irradiation field is narrowed to the stimulable phosphor sheet, scattered radiation rays enter the irradiation field and appear in the low-stimulated luminescence area on the histodarum. I love the field! ! It is preferable to use the minimum amount of stimulated luminescence light in the histogram within the irradiation field as the minimum amount of stimulated luminescence light S in the histogram.

In the above histogram, the range from the minimum stimulated luminescence light intensity Sl to the predetermined stimulated luminescence light intensity value determined by the imaging conditions means that the bare area is the area excluding the body part and skin area, and is the range necessary for bone diagnosis. It means a part, that is, a bone part or a range of a bone part and the surrounding muscle part. Such a predetermined stimulated luminescence light amount value can be determined with some degree of accuracy based on imaging conditions such as the imaging site and imaging method. This is because the pattern of the look-ahead histogram is determined to some extent depending on the area to be imaged and the imaging method, and by referring to the pattern of the histogram that is determined to some extent, it is possible to determine which range of stimulated luminescence light intensity values should be adopted. can be easily determined.

Predetermined stimulated luminescence light ff determined by this photographing condition
To list some specific examples of the i value, the following method according to the invention is a method of determining reading conditions based on the histogram portion (desired image information range portion in the histogram) obtained as described above. , there are various possible methods for determining this, but one of them, which is to obtain Smax and 3m1n of the desired image information range and determine the reading conditions based on these, will be described below.

First, from the look-ahead histogram shown in the first quadrant of FIG. 4, the histogram portion over the range from the minimum value S1 to a predetermined value is determined as described above, and the maximum and minimum stimulated luminescence light 13maX of this histogram portion is calculated. and 3
Find min (3s+in -31). Since the pattern of the histogram varies to some extent depending on the region to be imaged and the method of imaging, the above-mentioned histogram portion ratio can be determined from the histogram with reference to the region and method to be imaged.

On the other hand, in the radiation image information recording and reproducing system which is the premise of the method according to the present invention, as described above, the main reading means obtains an electrical image signal from the stimulated luminescent light according to the reading conditions,
This signal is subjected to various signal processing by an image processing means, especially gradation processing according to gradation processing conditions determined depending on the imaged area and imaging method, and this signal is reproduced and recorded as an output image on a photosensitive material etc. . In this output image, there is a density range suitable for observation and interpretation, and generally this appropriate density range (Dmax-Qmin) is predetermined, and the desired gradation processing conditions are also predetermined. , an input signal level range (Qmax) to the image processing means corresponding to the appropriate density range (Dmax-Qmin);
x-Qmin) is uniquely determined according to this gradation processing condition (see Figure 4, which shows the relationship between the stimulated luminescence light amount and the output image density in a radiation image information recording and reproducing system using the method according to the present invention). ).

Therefore, the reading conditions may be determined so that Bmax and Sm1n obtained as described above correspond to Qmax and Qmin determined as described above.

In this case, the reading conditions are expressed by the input/output conversion curve in the second quadrant of FIG. 4, and specifically include the reading gain, scale factor, etc., and these may be determined as shown in the equation below.

QlaX -Qmin scale factor, -11111-S wax
-S sin Reading gain -f (Sk) In other words, the above scale factor indicates the slope of the line indicating the reading conditions in Fig. 4 (arrow H in the second quadrant of Fig. 4), and the The size of the range of emitted light amount is 3max-8
By changing the scale factor according to Qmax-, the range of the input signal level to the image processing means is changed to the range of the desired input signal level.
Qmin). Note that kl is a constant for matching the size of the range of unit stimulated luminescence light amount to the size of the range of unit desired input signal level.

Furthermore, the above-mentioned reading gain indicates the left and right positions of the line indicating the reading conditions (arrow I in the second quadrant in Fig. 4), and is the order of the range of the stimulated luminescence amount! ! (In the above formula, the predetermined light emission amount Sk on the histogram is used as a factor indicating this position.) By changing the reading gain according to can be matched to a range of positions.

If the reading conditions are determined as described above, the input range of the radiation image information signal by main reading to the image processing means will always be constant, and image processing will be simplified.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are diagrams showing the histogram portion calculated from the minimum stimulated luminescence light amount value S1 in the look-ahead histogram to a predetermined value determined by the photographing conditions, respectively. FIG. 3 is a diagram showing the relationship between a histogram and an output image. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] A stimulable phosphor sheet on which radiation image information of a subject is stored and recorded is scanned with excitation light, and stimulated luminescence light emitted from the sheet is read by a photoelectric reading means to produce an image signal for visible image reproduction. Prior to the actual reading to obtain the actual reading, the sheet is scanned in advance with excitation light at a lower level than the excitation light used for this actual reading to obtain a histogram of the amount of stimulated luminescence emitted from this sheet. In the radiation image information reading condition determining method, the reading conditions for performing the main reading are determined based on the histogram obtained by reading, in which the reading conditions are determined based on the minimum amount of stimulated luminescence light in the histogram obtained by the pre-reading. 1. A reading condition determining method, characterized in that the reading condition determination method is carried out based on a histogram portion ranging from a value to a predetermined value determined by photographing conditions.